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Working out the rate flow

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This might help out from an earlier thread on here.

Have a look at this calculator:


I've just set up my 4x18x20 on a sump and i used 2x 1" (25mm) drains. The calculator said 1x 1" was enough for my flow rate but i went with 2 so if one gets blocked the other can still handle full flow. For the return I used 3/4" (19mm) as this fitted onto the outlet of my pump.

Hope that helps at least a little.


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work out how many liters your tank holds then multiply that by 4 or 6 depending on how many times u want the water turned over and get a pump thats somewhere near close

as for the hole size/bulkhead requirements if ya want gurgling noises like when u pull the plug on the bath go small and not enough

seriously that site has no idea its assumes that you get a totally full return pipe at optimum pressure load of bollox experience tells me 25 mm x2 will work if your running a 12-1500 lph pump and not much more and even this will struggle to cope, the site u mentioned says for my 3500lph pump i need 1 x 32 mm bulkhead = fail / dry sump gurgling noises i actually needed 2 x32 . on my 2500lph pump i have 3x20 mm i started with 2 and ended up adding the 3rd and they struggle but i have silenced them to what they were b4 the 3rd was added

end of the day do your self a favor use that site by all means but double what they say

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